Rebreather Diving

A Rebreather is provides a breathing gas containing oxygen and recycles exhaled gas. This recycling reduces the volume of breathing gas used, making a rebreather lighter and more compact than an open-circuit breathing set for the same duration in environments where humans cannot safely breathe from the atmosphere.

Oxygen rebreather

This is the oldest type of rebreather and was commonly used by navies from the early twentieth century. The only gas that it supplies is oxygen. As pure oxygen is toxic when inhaled at pressure, oxygen rebreathers are limited to a depth of 6 meters.

Semi-Closed Circuit Rebreather SCR

Military and recreational divers use these because they provide good underwater duration with fairly simple and cheap equipment. Semi-closed circuit equipment generally supplies one breathing gas such as air or nitrox or trimix. The gas is injected at a constant rate. Excess gas is constantly vented from the loop in small volumes. The diver must fill the cylinders with gas mix that has a maximum operating depth that is safe for the depth of the dive being planned. As the amount of oxygen required by the diver increases with work rate, the oxygen injection rate must be carefully chosen and controlled to prevent either oxygen toxicity or unconsciousness in the diver due to hypoxia.

Closed-Circuit Rebreather CCR

Military, photographic and recreational divers use these because they allow long dives and produce no bubbles. CCRs generally supply two breathing gases to the loop: one is pure oxygen and the other is a diluent such as air, nitrox or trimix.
The major task of the closed circuit rebreather is to control the oxygen concentration (oxygen partial pressure), in the loop and to warn the diver if it is becoming dangerously low or high.